Although nearly half of all adults in the United States (95 million) have high blood pressure (BP), only one in three patients can successfully control their high BP with conventional treatment, including lifestyle modifications and, if needed, antihypertensive medication. Stress is known to increase BP in at least two ways: (1) activating the sympathetic nervous system to make the heart pump harder and the blood vessels constrict, and (2) interfering with health behaviors, including diet, exercise, and sleep. Mindfulness-Based Stress Reduction (MBSR) is a proven meditation program to reduce stress. In our in-press trial (R21 AT002698-01A2) on adults with unmedicated prehypertension, an 8-week MBSR program significantly lowered high BP. The current R01 application proposes a two-site randomized clinical trial (RCT) with a larger, more diverse sample of adults from Cleveland, OH, and Durham, NC. We will also test a conceptual model that emphasizes decentering as a key mechanism by which MBSR reduces the impact of acute and chronic stress on high BP. Decentering is the ability to observe stress-related thoughts, emotions, and impulses in a way that allows one to disengage from automatic reactions to stress, maintain one's focus of attention, and respond to a demanding task or stressful trigger more effectively. We expect that MBSR-related gains in decentering will reduce exaggerated cardiovascular reactivity to mild emotional stress, expedite physiological recovery, and increase healthy lifestyle behaviors over time. We plan to enroll 180 unmedicated adults with prehypertension who will receive lifestyle modification advice. Patients will then be randomly assigned to one of three study arms over an 8-week intervention period: (1) MBSR training; (2) Stress Management Education (SME), a credible, active comparison group that controls for instruction time, attention from class instructors, social support, and homework assignments, but without the active ingredient of mindfulness meditation; or a wait-list control (WLC) group that controls for natural history of changes in high BP while patients complete the study assessments only. Assessments of clinic BP (primary outcome), 24-hr ambulatory BP, stress-induced cardiovascular reactivity including heart rate (HR), BP, cardiac output (CO), pre-ejection period (PEP), and vascular resistance, and objective behavioral reactions to a mild emotional stressor will occur at Weeks 0 (baseline), 8 (post-treatment), and 60 (one-year follow-up). In addition, clinic BP will be assessed at Weeks 4 (mid-treatment) and 34 (six-month follow-up). Health behaviors will be assessed at each time point. Waitlist patients will be invited to receive their choice of open-label MBSR or SME-allowing us to explore the effect of patient preference on intervention effect sizes. The proposed two-site RCT will address two critical public health needs: (1) the need for high-quality trials wih longer-term follow-up to definitively test the effectiveness and durability of mindfulness meditation for lowering BP, and (2) the need to discern the specific psychological, biological, and behavioral mechanisms by which mindfulness meditation may reduce high BP.